1. (Field of the Invention)
The present invention relates to a plastic container closure and to a method of producing the same. More specifically, the invention relates to a plastic container closure with liner featuring high sealing precision, excellent sealing performance to the mouth of the container and, particularly, excellent shock-resistant sealing performance and pressure-resistant sealing performance, and to a method of producing the same.
2. (Description of the Prior Art)
In recent years, metal container closures have been replaced by plastic container closures for hermetically sealing the mouths of plastic bottles and glass bottles owing to their merits of easy disposal and recycled use.
Some plastic container closures use, as the sealing material, the synthetic resin itself that is forming the inner surface of the top panel of the container closure. From the standpoint of obtaining hermetically sealing performance and, particularly, pressure-resistant sealing performance, however, it is desired to employ a liner or a packing that is excellent in softness and cushioning property.
Japanese Patent Publications Nos. 44627/1988, 48704/1988 and 8141/1994 are disclosing container closures provided with a liner, wherein provision is made of an inwardly extending annular liner-holding member on the inner surface of a skirt portion which is integrally continuous to the outer peripheral edge of the top panel, so that the liner will not escape from the closure shell.
Furthermore, Japanese Patent Publication No. 13349/1994 discloses a plastic container closure having a packing provided in the closure shell and further having a plurality of annular ribs formed on the top panel of the container closure.
According to the former-method of providing an annular liner-holding member on the inner surface of the skirt portion, however, a portion of the annular holding member of the container closure shell must be forcibly released at the time of molding the container closure shell and, hence, the annular liner-holding member must have a reduced thickness. In press-molding the liner, therefore, the annular holding member is deformed in an undulated manner at the time of bringing the outer sleeve of the molding tool and the annular holding member into engagement together, whereby the liner leaks outwardly or it becomes difficult to strictly control the size of the sealing portion on the outer periphery of the liner.
The container closure used for the contents that produce pressure loses pressure-resistant sealing performance due to its buckling deformation at the top panel portion. It is therefore desired to accomplish the sealing along the outer peripheral portion of the mouth of the bottle rather than at the top of the mouth of the bottle. The above-mentioned former container closure, however, does not permit to establish even such a sealing structure.
On the other hand, the latter container closure is satisfactory from the standpoint of accomplishing the sealing along the outer peripheral portion of the mouth of the bottle, but requires cumbersome operation for fitting the packing piece by piece into a number of container closures. Besides, the packing that is fitted may often escape, which is not still satisfactory from the viewpoint of operability.